【作者】 于小丹；

【导师】 郭伊荇；

【作者基本信息】 东北师范大学 ， 物理化学， 2008， 博士

【摘要】 本论文致力于耐水性多金属氧酸盐的合成与表征,并针对所合成的耐水性多金属氧酸盐的特点,选用不同类型的催化反应（酸催化、氧化催化和光催化）,分别考察了这些材料在非均相催化反应中的性能。首先利用溶胶-凝胶结合程序升温的溶剂热方法,制备了具有光催化活性的二氧化钛负载型酸式钨磷酸铯盐Cs_xH_3-xPW₁₂O₄₀/TiO₂（x = 0.5、1.0、1.5、2.0、2.5和3.0）复合材料。通过紫外–可见光谱、红外光谱、拉曼散射光谱和X射线粉末衍射等表征手段对所合成材料的晶相结构和光吸收性质进行了结构表征。经研究发现,形成复合材料后,母体酸式钨磷酸铯盐的基本结构仍然保留,而且与载体二氧化钛之间通过化学作用相结合,这种强的化学作用导致酸式钨磷酸铯盐分子被牢固地束缚在二氧化钛网络上。利用扫描电镜以及吸附测定等表征手段对复合材料的形貌以及表面物理化学性质进行了表征。结果表明,Cs_xH_3-xPW₁₂O₄₀/TiO₂具有介孔结构以及较好的表面物理化学性质（BET比表面积较高、孔径较大且均匀分布）。通过水溶液中三种有机污染物（对硝基苯酚、甲基橙和罗丹明-B）的紫外光光催化降解反应,系统研究了不同铯与氢摩尔比时得到的Cs_xH_3-xPW₁₂O₄₀/TiO₂的光催化活性差异,并与母体Cs_xH_3-xPW₁₂O₄₀和商用二氧化钛光催化剂（P25）进行了比较。实验结果表明,Cs_xH_3-xPW₁₂O₄₀/TiO₂的光催化活性高于母体Cs_xH_3-xPW₁₂O₄₀和P25。Cs_xH_3-xPW₁₂O₄₀/TiO₂的较高光催化活性源自此复合材料的光吸收特性、表面物理化学性质、表面酸性以及Cs_xH_3-xPW₁₂O₄₀和TiO₂之间的协同作用。然后,利用沉淀法合成了一系列Dawson型酸式钨磷酸铯盐Cs_xH_6-xP₂W₁₈O₆₂（x = 1.5、2.0、2.5、3.5、4.5和6.0）和Keggin型酸式钨磷酸铯盐Cs_xH_3-xPW₁₂O₄₀（x = 1.0、1.5、2.0、2.5和3.0）,并通过紫外-可见光谱、红外光谱、X射线粉末衍射、X射线光电子能谱以及吸附测定等表征手段对它们的晶相结构和表面结构进行了表征。通过由生物平台分子乙酰丙酸合成双酚酸的反应,系统地研究了Cs_xH_6-xP₂W₁₈O₆₂的酸催化活性,并与母体Cs_xH_3-xPW₁₂O₄₀及传统酸催化剂HCl、HZSM-5和MCM-49进行了比较。除此之外,还对催化剂对反应分子的吸附行为以及影响酸催化活性的诸多因素如溶剂、催化剂用量、反应物之间的摩尔比、反应温度、搅拌速度以及反应时间进行了深入的研究。通过对以上两类多酸盐的催化性能的研究,发现在无溶剂条件下对于合成双酚酸的反应,Cs_1.5H_4.5P₂W₁₈O₆₂和Cs_2.5H_0.5PW₁₂O₄₀在Dawson型多酸盐及Keggin型多酸盐中分别具有最高的催化活性;另外,Dawson型多酸盐Cs_xH_6-xP₂W₁₈O₆₂的催化活性和选择性均高于Keggin型多酸盐Cs_xH_3-xPW₁₂O₄₀。这两类催化剂的不同催化活性源自于其具有不同的催化行为,文中对引起催化行为差异的原因进行了解释。最后,采用非离子表面活性剂（P123）为结构导向剂,通过溶胶-凝胶和程序升温溶剂热等方法,制备了新型介孔结构二氧化硅负载型双缺位钨硅酸盐[（n-C₄H₉）-4N]₄[γ-SiW₁₀O₃₄（H₂O）₂]/SiO₂复合材料,其中,双缺位钨硅酸盐的担载量为4.3-14.8%。通过红外光谱、拉曼散射、低（高）角度X射线粉末衍射、31Si固体核磁共振光谱、吸附测定以及高分辨透射电镜等表征手段对所合成的复合材料进行了表征。结果表明,双缺位钨硅酸盐与载体二氧化硅网络连接形成复合材料后,其基本的Keggin结构仍然保留,而且与载体二氧化硅之间通过W-O-Si共价键相结合,从而保证双缺位钨硅酸盐分子与载体之间牢固结合;另外,此复合材料具有三维交联孔结构,表现出优异的表面物理化学性质如大比表面积、高孔体积、较大孔径以及催化活性点位均匀分散在载体中。通过苯乙烯的环氧化反应对[（n-C₄H₉）₄N]₄[γ-SiW₁₀O₃₄（H₂O）₂]/SiO₂的氧化催化活性进行探究,其中使用H₂O₂（30%）做为氧化剂,发现此类复合材料对苯乙烯环氧化反应具有较好的催化活性。催化过程中,对影响催化活性的诸因素如溶剂、苯乙烯和H₂O₂的摩尔比及双缺位钨硅酸盐的担载量等因素进行了研究,并对决定[（n-C₄H₉）₄N]₄[γ-SiW₁₀O₃₄（H₂O）₂]/SiO₂氧化催化活性的主要原因进行了合理解释。更多还原

【Abstract】 Water-tolerant polyoxometalates were prepared and characterized. Based on the characteristic of prepared water-tolerant polyoxometalates, the catalytic activity of these catalysts were studied by three kinds of catalytic reactions.Firstly, nanocomposite photocatalysts, cesium hydrogen salts of 12-tungstophosphoric acid coupled with anatase TiO2 (Cs_xH_3-xPW₁₂O₄₀/TiO2, x = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0, respectively), were prepared via one-step sol–gel method followed by solvothermal treatment. The phase structure and optical absorption properties of the composites were characterized by several characterization techniques including FT-IR, XRD and Raman scattering spectroscopy. The results indicated that the primary Keggin structure of starting POM in as-prepared composites remain intact after formation of the composites, and the strong chemical interactions between POM molecules and titania network existed. The morpholygy and surface textural properties of the prepared composites were characterized by FESEM and N2 adsorption/desorption analysis, indicating Cs_xH_3-xPW₁₂O₄₀/TiO₂ composites had excellent surface physicochemical properties （mesoporosity, large BET surface area and uniform pore size）. The photocatalytic activities of Cs_xH_3-xPW₁₂O₄₀/TiO₂ were evaluated by the degradation of three model organic molecules including 4-nitrophenol （4-NP）, methyl orange （MO）, and rhodamine B （RB） under UV-light irradiation. For comparison, the photocatalytic activityies of the parent CsxH3?xPW12O40 and Degussa P25 were studied under the same conditions. The results showed that as-prepared nanocomposite photocatalysts were substantially more effective than the starting CsxH3?xPW12O40 and Degussa P25. The high photoactivities of as-prepared nanocomposites could be attributed the higher surface acidity, mesoporosity, and the synergistic effect existed between the CsxH3?xPW12O40 and the TiO2 matrix.Secondly, a series of water-tolerent cesium partly substituted Dawson type heteropolyacids, Cs_xH_6-xP₂W₁₈O₆₂ （x = 1.5, 2.0, 2.5, 3.5, 4.5, and 6.0）, and cesium partly substituted Keggin type heteropolyacids, (Cs_xH_3-xPW₁₂O₄₀, x = 1.0, 1.5, 2.0, 2.5, and 3.0), were synthesized and characterized using the techniques including UV-vis/DRS, FT-IR, XRD, XPS, and N2 porosimetry. As the unique and reusable solid acid catalysts, Cs_xH_6-xP₂W₁₈O₆₂ salts were applied to produce diphenolic acid by the condensation reaction of phenol with bio-platform molecule, levulinic acid. For comparison, Cs_xH_3-xPW₁₂O₄₀ （x = 1.0?3.0）, HCl, HZSM-5, and MCM-49 were also tested. Adsorption behavior of the catalysts and the influence factors on the catalytic activity and selectivity including solvent, molar ratio of phenol to levulinic acid, amount of catalyst, reaction temperature, stirring speed, and reaction time were considered. The experimental results demonstrated that both Cs_1.5H_4.5P₂W₁₈O₆₂ and Cs_<sub>2.5H_0.5PW₁₂O₄₀ exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity of Cs_xH_6-xP₂W₁₈O₆₂ were higher than those of Cs_xH_3-xPW₁₂O₄₀. Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated.Lastly, the mesoporous composites, [（n-C₄H₉）₄N]₄[γ-SiW₁₀O₃₄（H₂O）2]/SiO₂ (TBA-1^*/SiO₂, where TBA-1^* = [（n-C₄H₉）₄N]₄[γ-SiW₁₀O₃₄（H₂O）₂]), with TBA-1^* loading of 4.3-14.8% were prepared by sol–gel method followed by solvothermal treatment in the presence of triblock copolymer surfactant （P123）. The as-prepared composites were characterized by ICP-AES, FT-IR, XRD, Raman scattering spectroscopy, 31Si （MAS） NMR, TEM, and N2 adsorption/desorption analysis. The results indicated that the primary Keggin structure of parent TBA-1^* in as-prepared composites remain intact after formation of the composites, and the strong chemical interactions between TBA-1^* molecules and silica network existed. The materials exhibited excellent surface physicochemical properties including higer BET surface area, larger interconnected pore structure, and uniform pore size distribution. As-prepared TBA-1^*/SiO₂ were used as the heterogeneous oxidation catalyst for the styrene epoxidation reaction to synthesize styrene oxide in the presence of dilute H2O₂ （30%）. In addition, influences of solvent, molar ratio of styrene to H2O₂, TBA-1^* loading on the styrene conversion, styrene oxide yield and selectivity were considered.更多还原